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Defined in header <filesystem> | ||
template<> struct hash<std::filesystem::path>; | (since C++17) | |
The template specialization ofstd::hash forstd::filesystem::path allows users to obtain hash values ofstd::filesystem::path.
Theoperator() of this specialization isnoexcept. For everystd::filesystem::path valuep,std::hash<std::filesystem::path>{}(p) is equal tostd::filesystem::hash_value(p).
This specialization was absent from the C++17 standard publication, seeLWG issue 3657.
#include <cassert>#include <cstddef>#include <filesystem>#include <iomanip>#include <iostream>#include <unordered_set>namespace fs= std::filesystem; void show_hash(fs::pathconst& p){std::cout<<std::hex<<std::uppercase<<std::setw(16)<<std::hash<fs::path>{}(p)<<" : "<< p<<'\n';} int main(){auto tmp1= fs::path{"/tmp"};auto tmp2= fs::path{"/tmp/../tmp"};assert(!(tmp1== tmp2));assert(fs::equivalent(tmp1, tmp2)); show_hash(tmp1); show_hash(tmp2); for(auto s:{"/a///b","/a//b","/a/c","...","..",".",""}) show_hash(s); std::unordered_set<fs::path,std::hash<fs::path>> dirs{"/bin","/bin","/lib","/lib","/opt","/opt","/tmp","/tmp/../tmp"};for(fs::pathconst& p: dirs)std::cout<< p<<' ';std::cout<<'\n';}
Possible output:
6050C47ADB62DFE5 : "/tmp"62795A58B69AD90A : "/tmp/../tmp"FF302110C9991974 : "/a///b"FF302110C9991974 : "/a//b"FD6167277915D464 : "/a/c"C42040F82CD8B542 : "..."D2D30154E0B78BBC : ".."D18C722215ED0530 : "." 0 : """/tmp/../tmp" "/opt" "/lib" "/tmp" "/bin"
(C++11) | hash function object (class template)[edit] |
(C++17) | calculates a hash value for a path object (function)[edit] |
